Process of aging tubes



May 17, 1966 E- s. WENNIN PROCESS OF AGING TUBES Filed June 26, 1961 INVENTOR Ernesf .5. We/m/n ATTORNEY .United States Patent 3,251,640 PROCESS OF AGING TUBES Ernest S. Wennin, Emporium, Pa., assignor to Sylvania This invention relates to a process for aging electron tubes and to a mechanism for carrying out the process.

In the manufacture of electron tubes, a common method is to assemble the electrodes and a getter'on a stem, and subsequently assemble the stem with a bulb in order to envelop the electrodes. Either the bulb or the stem are provided with an exhaust tubulation to enable evacuation of the bulb and stemassembly after the bulb and stem have been sealed to each other. During evacuation of the Whole assembly on a machine known in the trade as a Sealex; i.e., a combined sealing and air exhausting machine, it has been the practice to apply a voltage to the filament to heat the cathode and surrounding areas in order to drive off gases occluded in surfaces within the tube. Also, induction coils have been placed about the exterior of the tube to heat the electrodes Within the tube and flash the getter, all while the filament within the tube has a voltage applied to it. After suitable heating and evacuation of the assembly, the exhaust tubulation is sealed olf.

However, the tubes thus produced have variable electrical characteristics with respect to each other and each tube would have unstable characteristics if immediately used in'electrical equipment. The unstable condition of the tube during early life is thought to be due in part to the release within the tube of gaseous agents or contaminants poisonous to the emissive coating on the cathode. During the early life of the tube, the electrodes, particularly the anode, when heated to elevated temperatures upon bombardment of electrons, release from these elec-- trodes certain occluded gas agents in the contaminants which migrate to the cathode and reduce the emission.

Therefore, in the prior art, the tubes after assembly of parts and initial heating and evacuation on the .Sealex, are immediately thereafter placed on an aging rack, whereon the filaments in the tube are subjected to varying voltage conditions in accordance with a fixed schedule, While suitable potentials are applied to the electrodes within the tube to improve and stabilize the tube characteristics.

Certain types of tubes so aged display degrees of electrical instability during the early part of the subsequent use thereof. It has been found that during approximately the first fifteen minutes of such use, a decided change may be noted in specific electrical characteristics of the tube. For example, in the case of a type 6BZ7 electron tube, a dip in excess of percent in the transconductance curve may exist at the end of fifteen minutes, the transconductance coming back to normal steady operating value after approximately forty hours of normal use. Where this dip at the end of fifteen minutes is greater than 15 percent, it has been cause for tube rejection since such a tube might in still further life beyond forty hours develop poor emissive characteristics, besides having low transconductance in its early life.'

Normal aging techniques involve the insertion of tubes to be aged into sockets on rack bars carried between a pair of endless indexible conveyors, and applying suitable voltages to the filaments and the various electrodes of the tubes. For an example of this procedure, reference may be had to the patent to Bussom et al. 2,943,904.

This invention contemplates superimposing upon the normal procedure the heating of electrodes within the tube from an external source.

.patent.

3,251,649 Patented May 17, 1966 It is an object of this invention to improve the tube aging process and mechanism so that a greater degree of tube consistency and electrical stability can be achieved whereby there are fewer tube rejects because of undue initial characteristics changes.

Another object of the invention is to render the aging process less costly than heretofore.

The foregoing objects are achieved in one aspect of the invention by providing an auxiliary tube aging mechanism and process whereby regulated heat is imparted to the tubes during a selected portion of the aging process. This procedure accomplishes greater uniformity in the stabilization of tube electrical characteristics and results in a better quality tube product without increasing the manufacturing time cycle.

For a better understanding of the invention reference is made to the following specification taken in conjunction with the accompanying drawing in which:

FIG. 1 is an elevation of an aging conveyor with parts broken away for clarity;

FIG. 2 is a view taken along line 2-2 of FIG. 1; and

FIG. 3 is a fragmentary back view of one of the bars of the aging conveyor.

Referring to the drawings with greater particularity, at 10 is illustrated the movable bars in an aging conveyor 11, for example, of the type disclosed in the Bussom et al. patent referred to heretofore, the bars being provided with tube sockets 12 into which the tubes 14 to be aged are plugged. The sockets, as disclosed in the Bussom et al. patent each have contacts therein connected by printed circuitry to shoes 15 on the backs of the bars, these shoes contacting insulated spring contacts 16 on the frame. The spring contacts are connected to suitable sources of voltage including a voltage supply (not shown) for the socket contacts to energize the filaments in the tubes. The electron tubes 14 having electrode elements enclosed in a conventional transparent glass wall, are plugged into sockets in a bar of the conveyor. The bars index from one position to the next in accordance with a prescribed schedule.

While the bars 10 move in their endless path, voltages are applied to the filaments and other electrodes of the tubes 14 in any manner known to the prior art, as, for example, in the manner indicated in the Bussom et al.

The cathode for the tubes may be of the indirectly heated type comprising a sleeve coated with emissive material and an internal heater, or of the emissively coated filament type.

, However, in accordance with this invention, a different aging technique is utilized from that employed in the prior art at one or more positions of the bars.

The auxiliary aging structure hereinafter described may be positioned in any number of locations on the aging ra'ck dependent upon the results desired in conjunction with special aging schedules for specific tube types. In this particular instance, for tube type 6BZ7, two positions of the ager are used at approximately three fourths of the way through the aging schedule. In FIG. 2 there is mounted on the ager 11 a support 17, this support comprising, at each end, a pair of straps 18 secured to the frame of the ager 11. A pair of angle bars 20, one for each pair of straps, are secured to the straps and cross angle bars 22 are also secured to the straps. To these cross angle bars are fastened the angledover ends of base plates 24, one each for each of the spaces laterally between sockets 12 on an ager bar 10. Mounted on each base plate is a socket 26 for a heating unit to heat the electrode elements in the tube. The unit may partake of any desired form, preferably a reflector type lamp 28. These lamps are positioned, while in use, substantially midway of the height of the tubes 14 by being plugged into their rack bar sockets 26. The re- 3 fiector lamps 28 are of a type formed to produce a large amount of heat from their filaments 31 and each lamp is provided with a reflector 30 to concentrate the light of the filament, and therefore its heat, upon a point along the longitudinal center of a tube 14 being processed on the ager. The degree of lamp heat may be controlled by variably adjusting the lamp voltage supply as desired.

It will be noted, see FIG. 1, that the reflectors in ad jacent lamps of an upper row are preferably directed in pairs toward each other so that the electrode elements in tubes 14 in alternate sockets 12 in that row in an ager bar are strongly heated, the remaining tubes in the remaining sockets of that row being similarly heated by pairs'of lamps 28 at the next lower indexed position of said bar. These lamps 28 are constantly energized and a large amount of high heat impinges on the tube 14 electrodes in line with the heat rays from the reflectors 30.

Thus, each tube 14 on the aging rack is subjected to high temperatures from a source external to the tube for a given period of time. This results in .reducing the slump in transconductance in the early life of the tube so that there are fewer rejects because of early life low transconductance.

Excellent results have been attained using a large range of temperatures. For some types of tubes the best results have been those using temperatures in the 200400 C. range. Others react better to higher temperatures. Good results, however, are found in all types tested within the 2001100 C. range. To prevent any getter on the bulb from giving off gases or vaporizing, it is desirable not to exceed a temperature of 400 C. in the glass, which limit can be adhered to even with the internal electrodes having temperatures of 1100 C. and above. If necessary, fans or nozzles may be mounted on the support 1 6 to cool the bulbs.

With normal prior art aging where the cathode heating filament is energized practically throughout the entire travel of the electron tube through the aging machine, and Where the filament is subjected at practically all times to normal opera-ting voltage or voltages in excess of normal, the transconductance has a tendency to slump initially, with the slump in many tubes being greater than an acceptable 15 percent in 15 minutes. With the present invention it has been found that the slump in trans conductance beyond the 15 percent level has been virtually eliminated. It also appears that where the initial slump is not too severe, only a reduced voltage need be applied to the filament during application of external heating to attain desirable transconductance at the end of a quarter hour. It has been found that as a result of utilizing the external application of heat tothe tubes, the speed of run of the aging conveyor may be accelerated, resulting in much saving of time and saving in the amount of energy applied to the tubes during the aging process. Also, the need for operating tubes at over-rated filament voltages is reduced, thereby reducing rejects of the type resulting from burned-out filaments.

Although several embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

Having thus described the invention, What is claimed is:

1. The processing of electron tubes having electrodes including a filament in heat conductive relationship to an emissive coating and an anode, which comprises heating and evacuating a tube, sealing ofl the tube and subjecting the tube to an aging process including the step of heating the anode from a source exterior to the electron tube.

2. The processing of electron tubes having electrodes including a filament in heat conductive relationship to an emissive coating and an anode, which comprises heating and evacuating a tube, sealing off the tube and subjecting the tube to an aging process including heating of the tube from a source exterior to the electron tube.

3. The processing of electron tubes having electrodes including a filament in heat conductive relationship to an emissive coating and an anode, which comprises heating and evacuating a tube, sealing ofi" the tube and subjecting thetube to an aging process including heating of the tube by energization of the filament therein and by concentrated heat applied to the anode from a source of heat external of the tube.

4. The processing of electron tubeshaving electrodes including a filament in heat conductive relationship to an emissive coating and an anode, which comprises evacuating a tube while it is heated internally by its own filament, sealing off the tube and subjecting the tube to an aging process including heating of the tube by energization of the filament therein at a voltage below the voltage applied to the filament in normal use of the tube and by concentrated heat applied to the anode from a source of heat external of the tube.

References Cited by the Examiner UNITED STATES PATENTS 1,983,668 12/1934 Jones et a1. 3l61 X 2,435,475 2/1948 Stromeyer 316-l 2,583,029 1/1952 Townsend 316-1 2,773,731 12/1956 Chick et al 316-27 2,943,904 7/1960 Bussom et al. 31627 FRANK E. BAILEY, Primary Examiner.

LEON PEAR, Examiner. 

1. THE PROCESSING OF ELECTRON TUBES HAVING ELECTRODES INCLUDING A FILAMENT IN HEAT CONDUCTIVE RELATIONSHIP TO AN EMISSIVE COATING AND AN ANODE, WHICH COMPRISES HEAT- 